adv anced lo ad sh aring contro ls for compre …€¦ · the compressors in a coordinated manner,...
TRANSCRIPT
Why compressor networks?A compressor network is a compression system in which two or more
compressors operate together. A parallel compressor network has flex-
ibility to match the total supplied flow to a varying production demand.
A series compressor network is useful for achieving higher compres-
sion ratios required by the process.
Challenges in compressor load sharingControlling a compressor network requires consideration of overall
network performance and performance of individual machines. The
major process control task is to distribute the overall load between the
compressors while controlling a shared process parameter, such as
suction header pressure, discharge header pressure, or total header
flow. One known load sharing strategy is to designate a single com-
pressor to control the shared process variable and to base load the
other compressors. This simple load distribution is characterized by
constrained responsiveness to changes in flow achievable with one
swing machine, increased exposure of the swing machine to surge,
and frequent gas recycling of the swing machine with resulting lower
overall efficiency. Changes in the steady-state load distribution require
operator intervention to adjust the base-loaded machines.
Active load sharing strategies automatically distribute load across
the compressors in a coordinated manner, but these strategies require
more sophisticated control algorithms with data interdependencies. A
single failure in the active load sharing system can force it to fall back
to a simple load sharing scenario with all of its weaknesses. Typical
failures in load sharing systems include faults in the Master Controller
and failure of the process variable. To maximize the effectiveness of
an active load sharing system, the system should have fault tolerance.
Compressor Network Management SystemWoodward has leveraged decades of experience in power management
to design a compressor load sharing system that eliminates the typical de-
pendency on a Master Controller with its associated single points of failure.
Multi-Master vs Single MasterActive load sharing systems usually require a Master Controller to
manage a shared setpoint and to balance load among compressors.
Woodward’s Compressor Network Management System (WCNetMS)
AdvAnced LoAd ShAring controLS for compreSSor networkSAlex Benim and Brian Eldredge (Woodward Inc.)
Compressor 1
Example Of Equidistant Load Sharing Control StrategyFor Two Compressors in a Parallel Network
WCNetMS System Architecture
Compressor 2
uses a distributed Multi-Master Control Architecture, so a dedicated
Master Controller is not needed. WCNetMS allows any Performance
Controller on the network to be a Master Controller, eliminating this
single point of failure. Each controller is able to produce the master
setpoint, common to all compressors on the network. The controller
designated as the Setpoint Master owns the common master setpoint
and distributes it to the other controllers over the data network. If the
active Setpoint Master controller has a fault, the Setpoint Master des-
ignation automatically transfers to a standby controller. The operator
can re-assign the Setpoint Master designation during any mode of op-
eration. Load balancing logic is implemented in all controllers, so the
compressor network load distribution remains in balance even when a
single controller fails.
Load Sharing Data NetworkActive load sharing systems depend on a data network that shares
critical parameters between the Performance Controllers. Failure of the
data network can compromise availability of the system. WCNetMS max-
imizes availability by including two redundant CPU modules. All primary
CPUs are connected on the primary data network. The backup CPUs
are linked through a backup data network. The primary and backup data
networks are completely independent. Thus, a failure on either network
does not affect availability of the WCNetMS load sharing system.
Considerations For Process TransmittersThe transmitter for the shared process variable, which is often ex-
posed to harsh field conditions, can be a weak link in the system. WC-
NetMS supports multiple transmitters. To further maximize availability,
the signals from the redundant transmitters are wired to control hard-
ware of different compressors. The signals are shared over the data
network and each controller handles redundancy management. There-
fore, a failure of a single controller or transmitter will not compromise
the load sharing system.
Proven Turbomachinery Control PlatformSince the 1990s Woodward’s purpose-built high-availability Mi-
croNet™ Plus and MicroNet™ TMR platforms have been operating in
petrochemical facilities and power plants worldwide. Over 500 integrat-
ed turbine-compressor systems have been commissioned. WCNetMS
is engineered to run on MicroNet™ control systems.
Woodward_Advertorial_Oct15_CT.indd 1 9/21/15 2:43 PM
CompressorTech 2 October 2015